* Astronomy

The largest known swarm of red supergiant stars has been found near the central bulge of our galaxy. It offers a rare glimpse of massive stars on the verge of exploding.
Red supergiants are among the largest stars in the universe and in fact are second in size only to rare 'hypergiant' stars such Eta Carinae. Spanning several hundred times the diameter of the Sun, each could fit millions of Sun-like stars inside it.
These stellar titans are extremely rare. Only very massive stars, more than 10 times as heavy as the Sun, turn into red supergiants. And the red supergiant phase lasts just 100,000 years before ending in a supernova, a fleeting moment compared to the overall lifespan of the star.
Only about 200 red supergiants have been identified in our galaxy. In 2006, a team led by Don Figer of the Rochester Institute of Technology (RIT) in New York, NY, US, reported finding a massive cluster of thousands of stars that included 14 red supergiants the biggest collection of these rare stars then known.
Now, Ben Davies, also of RIT, and a team that includes Figer have identified an even larger group of 26 red supergiants.

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About 40 stars near the centre of this image are red supergiants, appearing yellow in this infrared image from the Spitzer Space Telescope. Warm dust in the region glows red. The blue oval with a pink outline at top left may be the result of an ancient supernova and the larger blue patch below centre is a stellar nursery
Credit : B Davies/RIT/NASA


Title: A massive cluster of Red Supergiants at the base of the Scutum-Crux arm
Authors: Ben Davies (RIT), Don F. Figer (RIT), Rolf-Peter Kudritzki (IfA, Hawaii), John MacKenty (STScI), Francisco Najarro (CSIC, Madrid), Artemio Herrero (IAC, Spain)

We report on the unprecedented Red Supergiant (RSG) population of a massive young cluster, located at the base of the Scutum-Crux Galactic arm. We identify candidate cluster RSGs based on {\it 2MASS} photometry and medium resolution spectroscopy. With follow-up high-resolution spectroscopy, we use CO-bandhead equivalent width and high-precision radial velocity measurements to identify a core grouping of 26 physically-associated RSGs -- the largest such cluster known to-date. Using the stars' velocity dispersion, and their inferred luminosities in conjunction with evolutionary models, we argue that the cluster has an initial mass of ~40,000\msun, and is therefore among the most massive in the galaxy. Further, the cluster is only a few hundred parsecs away from the cluster of 14 RSGs recently reported by Figer et al (2006). These two RSG clusters represent 20% of all known RSGs in the Galaxy, and now offer the unique opportunity to study the pre-supernova evolution of massive stars, and the Blue- to Red-Supergiant ratio at uniform metallicity. We use GLIMPSE, MIPSGAL and MAGPIS survey data to identify several objects in the field of the larger cluster which seem to be indicative of recent region-wide starburst activity at the point where the Scutum-Crux arm intercepts the Galactic bulge. Future abundance studies of these clusters will therefore permit the study of the chemical evolution and metallicity gradient of the Galaxy in the region where the disk meets the bulge.

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-- Edited by Blobrana at 22:23, 2007-08-09

Title: Old open clusters in the inner Galaxy: FSR1744, FSR89 and FSR31
Authors: Charles Bonatto, Eduardo Bica

We establish the nature and derive fundamental and structural parameters of the recently catalogued objects FSR1744, FSR89 and FSR31. This work intends to provide clues to constrain the Galactic tidal disruption efficiency, improve statistics of the open cluster parameter space, and better define their age-distribution function inside the Solar circle. Properties of the objects are investigated by means of 2MASS colour-magnitude diagrams and stellar radial density profiles built with field star decontaminated photometry. Diagnostic-diagrams for structural parameters are used to help disentangle dynamical from high-background effects affecting such centrally projected open clusters. FSR1744, FSR89 and FSR31 are Gyr-class OCs located at Galactocentric distances 4.0 - 5.6kpc. Compared to nearby OCs, they have small core and limiting radii. With respect to the small number of OCs observed in the inner Galaxy, the emerging scenario in the near-infrared favours disruption driven by dynamical evolution rather than observational limitations associated with absorption and/or high background levels. Internally, the main processes associated with the dynamical evolution are, e.g. mass loss by stellar evolution, mass segregation and evaporation. Externally they are, e.g. tidal stress from the disk and bulge, and interactions with giant molecular clouds. FSR1744, FSR89 and FSR31 have structural parameters consistent with their Galactocentric distances, in the sense that tidally induced effects may have accelerated the dynamical evolution.

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After pondering the weighty question of the mass of the Milky Way galaxy, astronomers have come up with an answer: 3 x 10⁴² kg.
That is, our galaxy weighs three times 10 to the power of 42 kilograms - a number written as 3 followed by 42 zeroes, which has echoes of author Douglas Adams's fictional answer to the question of life, the universe and everything in his series Hitchhiker's Guide to the Galaxy.

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Radioactive iron, a window to the stars
 
ESAs orbiting gamma-ray observatory, Integral, has made a pioneering unequivocal discovery of radioactive iron-60 in our galaxy that provides powerful insight into the workings of massive stars that pervade and shape it.
Since late 2002, Integral has been collecting data from across the galaxy. It shows an enhancement in gamma rays at two characteristic energies, 1173 and 1333 kilo electron Volts. These are produced by radioactive decay of iron-60 into cobalt-60. Found drifting in space, the radioactive isotope has been sought for long. All past reported sightings of iron-60 have been subject to controversy. Now Integral has provided unequivocal evidence.

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